Need your kids to pick their grades up? Tell them to spend less time on Facebook.

A new study released by Ohio State University shows that college students who use Facebook spend less time studying and have lower grades than students who don't use the popular social networking site. But don't count on the Facebook users admitting the problem. The university report noted that 79% of them said that using the social networking site was not interfering with their studies.

"We can't say that use of Facebook leads to lower grades and less studying -- but we did find a relationship there," said Aryn Karpinski, co-author of the study and a doctoral student in education at Ohio State University. "There's a disconnect between students' claim that Facebook use doesn't impact their studies, and our finding showing they had lower grades and spent less time studying."

And last month, Nielsen Online reported that social networks like Facebook had knocked e-mail down a rung in the ladder of leading online communication tools. Used by two-thirds of all worldwide online users, social networks and blogs have become the fourth most popular online products. The report now lists e-mail as No. 5 on the list of favorite online tools.

The Ohio State University study found that 85% of undergraduates use Facebook, while 52% of graduate students had accounts. It also found that Facebook users, who generally studied between one and five hours per week, had GPAs between 3.0 and 3.5, but nonusers, who studied 11 to 15 hours per week, had GPAs between 3.5 and 4.0.

And Karpinski pointed out that the study doesn't necessarily mean Facebook use automatically leads to lower grades.

"There may be other factors involved, such as personality traits, that link Facebook use and lower grades," she added. "It may be that if it wasn't for Facebook, some students would still find other ways to avoid studying and would still get lower grades. But perhaps the lower GPAs could actually be because students are spending too much time socializing online."